The present invention relates to a method of controlling diseases of seeds which have been infected with seed borne diseases.
Seeds for use in agricultural and horticultural production of, for example, vegetable crops, and ornamental plants, are produced in fields called as seed producing places, facilities such as green houses and plastic green houses. In these seed producing locations, seeds called as foundation seeds for use in producing seeds have been cultivated for seed production.
The seed production is to produce seeds for use in agriculture or horticulture from various kinds of foundation seeds. There is a case in which even when the thus produced seeds have a genotype to be targeted and sufficient germinating power, they are infected with diseases. Such diseases are called as seed borne diseases and are infected from mother plants which have been infected with diseases (Seeds Problems in Agriculture and Forestry, 161-183, Shun-ichiro Nakamura, Yokendo Ltd., 1985; Seed Quality Basic Mechanisms and Agricultural Implications, 160-171, Amarjit S Basra ed., Food Products Press, 1995). When seeds which have been infected with a seed borne disease are used for production of vegetable crops, not only an onset of the disease is exhibited from disease infected seeds, but also such seeds become an infectious source during a period of nursery or culturing to infect intrinsically disease-free seeds with disease whereupon production of vegetable crops is liable to be greatly damaged. Further, when a pathogen or a crop infected with a disease is left as remains in a soil of a field or in an installation of a green house or plastic green house, there are many cases in which onset of disease can be seen at the time of subsequent cultivation. Still further, more and more seeds of vegetables and seeds of ornamental plants have recently been exported. When seeds thereof are infected with a seed borne disease, they can not pass through quarantine so that they can not be exported or sold (Plant Pathogens and the World-Wide Movement of Seeds, Denis C. McGee, APS Press, 1997).
As described above, a loss in vegetable crops, seed sales or distribution business thereof which would be caused by the seed borne disease is extremely large so that it is a big problem to overcome such a disease in cultivation of seeds for seed production and seed sales (Ecology and Control of Seed Borne Diseases, Kan-ichi Ohata et al., Japan Plant Protection Assn., 1999; Seed Technology, Vol. 20, 2, 187-197, 1998).
A countermeasure which is taken at present is exemplified by sterilization of foundation seeds and sterilization of seeds obtained by seed production. The latter has widely been executed on a commercial basis. Included therein are, for example, soaking of seeds in an agrochemical solution, powder-coating or coating of seeds with an agrochemical, warm-water soaking of seeds, dry-heating treatment of seeds and other treatments (Seeds Problems in Agriculture and Forestry, 183-194, Shun-ichiro Nakamura, Yokendo Ltd., 1985). Although it is recognized that methods of such sterilizations are effective to some extent, sufficient sterilization effect can not always be obtained since sufficient sterilization will bring about reduction of germination rate of seeds and other problems.
Further, in recent years, a damage caused by the seed borne disease has rapidly been increased. It can not be denied that a reason thereof is attributable to the seed sterilization. This is because that, when the seeds are sterilized, not only pathogenic microorganisms but also ordinary microorganisms inhabiting on an outside surface of or inside the seed are reduced in number to a great extent whereupon a microbial air-pocket is generated in the seed, resulting in reducing a mutual suppression property in a biological field. Such reducing the mutual suppression property will permit survived pathogenic microorganisms even scarce in number to initiate infection thereby causing a severe onset of the disease. However, though the above-described features may be true, from the standpoint of controlling the seed borne disease, the seed sterilization can not all be excluded. This is because that the seed which is highly liable to be infected with pathogenic microorganisms has no other way to reduce a density of pathogenic microorganisms than by seed sterilization.
On the other hand, in recent years, in controlling plant diseases, apart from using synthetic agrochemicals, using effective microorganisms inhabiting in nature has been tried (New Strategy of Controlling Diseases, 141-188, Wataru Komada and Tadaoki Inaba et al., Zenkoku Nouson Kyouiku Kyoukai, 1992; Microorganism Technology for Protecting Agricultural Environment, Ienohikari Kyokai, 1998; Seed Technology, Vol. 20, 2, 198-208, 1998; Microbial Agrochemical, Masao Yamada et al., Zenkoku Nouson Kyouiku Kyoukai, 2000). The effective microorganisms to be utilized for such controlling diseases are those which are antagonistic against pathogens and suppress proliferation of the pathogens. Such effective microorganisms, being different from synthetic agrochemicals, proliferate on their own so that they hold a lasting controlling effect. Since they can suppress generation of agrochemical resistant microorganisms and inhibit in nature, they have an advantage in that there is almost no fear of causing an environmental pollution.
However, when the disease is viewed from a side of a disease controlling effect, it is a present state that there exists nearly no substance which exceeds agrochemicals. Reasons for it are generally summed up in two points as follows:
1. In a microbiological world abundant in diversity, microorganisms which are effective in suppressing only limited types of microorganisms, so-called pathogenic microorganisms are hardly fixed by being subjected to selection after treatment; and
2. Under a cultivation condition abundant in diversity, effective microorganisms are not always in an environment suitable for survival so that the controlling effect against pathogenic microorganisms can not always be consistently executed by a single-typed effective microorganisms. As a result, controlling effect to be aimed can not fully be obtained.
In order to overcome the above-described problems, efforts to generate an environment favorable for survival of the effective microorganisms have been executed. Namely, it is to find a method in which, when microorganisms are treated, materials called as a carrier (such as coral, peat moss, zeolite, vermiculite, perlite, and charcoal) or substrates as foods for effective microorganisms (such as rice husks, straws, paper pulp, crab shells, rice bran, and rape cakes) are added in order to provide effective microorganisms with a refuge that protects them from other ordinary microorganisms and changes of the environment whereupon the effective microorganisms stably survive (Control of Diseases by Antagonistic Microorganisms, 86-90, Toshio Kijima, Rural Culture Assn., 1992). As other methods, various proposals of soil treatments by effective microorganisms have been made (Japanese Patent Laid-Opens Nos. 56616/1994 and 106306/1999).
Further, a multiplicity of proposals have been made also in technologies of utilizing effective microorganisms for a purpose of controlling seed diseases (Japanese Patent Laid-Opens Nos. 51305/1993, 253827/1994, 25716/1995, 75562/1995, 224655/1997, 203917/1998, 4606/1999, and 253151/1999; U.S. Pat. No. 4,668,512; Annual Review of Phytopathology 31, 53-80, Cook, R. J., 1993; and Hort Technology, 345-349, 2(3), M. B. Bennett, V. A. Fritz, N. W. Callan, 1992).
However, there has not been developed a technology in which, in order to establish an environment favorable for survival of effective microorganisms in seeds, influence of ordinary microorganisms to the effective microorganisms is reduced and, at the same time, a contamination of seeds by pathogens is controlled to some extent by suppressing an amount of microorganisms inhabiting inside seeds by means of previously treating seeds by a physical or chemical technique and, thereafter, by treating the resultant seeds with effective microorganisms, particularly, a plurality of effective microorganisms, and, further, controlling of diseases are attempted to correspond to a change of cultivation environments.
Further, in International Patent Publication No. WO94/10845 (hereinafter referred to as WO94/10845), a synergistic microbicidal composition which comprises a strain belonging to the genus Pseudomonas as an effective microorganism and a specified agrochemical in combination have been proposed. However, in a case that treatments by the effective microorganism and the agrochemical are simultaneously performed as described above, the treatment methods of the effective microorganism and the agrochemical are same to each other whereupon respective optimal treatment methods by the effective microorganism and the agrochemical can not individually be selected from one another. Moreover, in such a simultaneous treatment, one of the agrochemical which gives no influence to the effective microorganism or the effective microorganism which has resistance to the agrochemical can only be utilized whereupon, even in WO94/10845, a combination which gives no influence to the effective microorganism by limiting types of effective microorganisms and agrochemicals has been selected.
The present invention has been attained under the above circumstances and has an object of providing a method of effectively controlling a seed borne disease from a seed of a vegetable and ornamental plant to obtain a desease-free seed of high quality.
As a result of an intensive study for overcoming the above-described problems, the present inventors have achieved the present invention by finding that, after a seed has been sterilized against a pathogenic microorganism which brings about a seed borne disease by a physical or chemical technique such as a dry-heating treatment and a treatment with a chemical substance, the seed is treated with an effective microorganism which is antagonistic against such a pathogenic microorganism thereby allowing to control a disease of the seed to be targeted.
That is, the method of controlling the seed disease of the present invention comprises the steps of: sterilizing the seed by a physical and/or chemical technique; and treating the seed with the effective microorganism which is antagonistic against such a pathogenic microorganism.
According to the method of controlling the seed disease, an infection by the pathogen of the seed borne disease can be suppressed to some extent by sterilizing the seed by at least one of physical and chemical techniques before treating it by the effective microorganism. Further, by suppressing an amount of the microorganism held by the seed by means of such sterilizing to some extent, an influence of an ordinary microorganism to the effective microorganism can be reduced thereby establishing an environment favorable for survival of the effective microorganism inside the seed. As a result, the effective microorganism which is provided to the seed after being sterilized can be fixed thereon without being selected thereby allowing to effectively exert a disease controlling effect.
Further, the method according to the present invention can select respective treatment methods of the effective microorganism and agrochemical separately different from the above-described simultaneous treatment method of the effective microorganism and agrochemical. Furthermore, according to the present-method, even when the seed has been sterilized by a chemical which has an influence to the effective microorganism, the influence of such a chemical to the effective microorganism can be suppressed as long as the chemical is provided to the seed by presoaking or other treatments. Therefore, the present method has a high degree of freedom in combination of physical or chemical technique for sterilization of the seed and the effective microorganism.
In the present invention, a so-called microbial air-pocket condition generated by the sterilization of the seed is avoided by actively contaminating the seed with the effective microorganism. On this occasion, even when a pathogenic microorganism exists in the seed to some extent after the seed has been subjected to sterilization, an establishment of an illustrative representation, namely, xe2x80x9cinfection readily goes to onsetxe2x80x9d, can be avoided as long as the seed is contaminated again with the effective microorganism which has a higher potential than that of an infection source of the pathogenic microorganisms (biological remediation of a seed microorganism ecology system). As described above, the present invention provides a technique for controlling the seed borne disease by executing an effective microorganism treatment on a partially sterilized seed.
In the method of controlling the seed disease according to the present invention, it is preferable that the above-described effective microorganism comprises a plurality of microorganisms. Namely, it is advantageous that the seed which has been sterilized by the physical or chemical technique is treated with at least two types of strains of effective microorganisms. By treating the seed with a plurality of effective microorganisms, a controlling effect against a pathogen can be exerted in a consistent manner even under a variety of cultivating conditions.